Magnetic transducing system



Jan. 9, 1962 w. R. JOHNSON MAGNETIC TRANSDUCING SYSTEM Filed April 14, 1959 5 Sheets-Sheet 1 Jan. 9, 1962 w. R. JOHNSON 3,016,416

MAGNETIC TRANsDucING SYSTEM Filed April 14, 1959 3 Sheets-Sheet 2 Jan. 9, 1962 w. R. .JOHNSON MAGNETIC TRANSDUCING SYSTEM 5 Sheets-Sheet 3 Filed April 14, 1959 3,016,416, ..4 MAGNETIC TRANSDUCING SYSTEM Wayne R.,.lolinson, Los Angeles, Calif., assignerV to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of -vDelaware ,l

Filed Apr. 14, 1959, SenNo. 806,369 6 Claims. (Cl. 178-6.6)

This invention relates to facsimile transmission systems and, more particularly, to receiving and reproducing systems for slow speed facsimile.

Facsimile transmission is the transmission by electrical means of any graphic material such as pictures, printed matter, etc. The graphic material is broken into sequential elementary parts which are electrically transmitted through a transmission medium and then at a receiving station assembled into a graphic representation of the original material.

In typical facsimile transmission systems, the graphic material or picture is scanned by mounting the graphic material on a revolving drum and projecting a small beam of light on to or through the material. The light from the picture is provided to a phototube which provides anelectrical signal proportional to the density of the graphic material. The beam of light is moved to progressively cover every spot ori the graphic material so that the output of the phototube is a sequentially arranged electrical representation of the graphic Imaterial. In some systems, the electrical representation of the graphic material is modulated .on a suitable carrier and in others the electrical representation is directly transmitted.

At the receiving end, the modulated signal isV demodulated and supplied to a reproducing system. There are a number of types of reproducing systems in use but, in general, they merely reverse the sequence at the transmitting end of the facsimile system. The varying electrical representation of the picture is utilized to provide a variable beam of light on light sensitive or photographic paper or it is utilized directly on a dry coated paper sensitized to electrical current passage.

The photographic process is generally preferred because any number of prints can be made from the recorded negative and because the dry coated papers do not fully record the contrast range of picture densities. Both the photographic process and the electrical direct recording process however, utilize special papers; the former photographic developing papers; and the latter dry coated papers such as papers coated with lead thiosulphate and titanium onide. The photographic process, moreover, is complicated and lengthy because the papers vmust be developed.

ln a specific embodiment of this invention, a facsimile reproducing system is provided which' does not require photoelectric or photographic equipment or dry coated papers. The reproducing system includes a high speed magnetic recorder which records a magnetic image of the transmitted graphic material on a moving magnetic recording tape.

The facsimile signals'are slow speed signals because of the slow speed of the scanning beam of lightr at the transmitter. Illustrative facsimile scanning speeds are 10 inches per second with 1:20 lines or scans across the graphic materialV being completed perminute. The magnetic recorder on the other hand has a recording speed ofV approximately 15,0% feet per second which is 18,000 times faster than the facsimile scanning speed.

The magnetic recorder includes a travelling wave transducer head of the type described in detail in` my co'- pending patent application Ser. No; 733,165v led on May 5, 1958. The travelling. wave transducer headA transversely records samples of the facsimile signals on United States Patent O ice 2 successive transverse tracks of the longitudinally moving magnetic tape. The transducer head which is stationary is provided with a 'tubular shape disposed in a transverse direction across the tape. Transverse recording is achieved even though the transducer head is stationary by exciting longitudinally elastic waves in the head whichr move transversely with respect to tlie longitudinal direction of the movement of the magnetic tape. The transducer head includes a magnetostrictive tube and the elastic waves momentarily relieve stresses normally in thetube so that, in effect, the elastic waves function as enabling waves by locally changing the permeability of the` tube. `The recording speed of the transducer head is the speed of the elastic waves.

The slow speed facsimile signals are sampled by an electronic switch and the sampled signals are introduced to a signal coil coupled to the magnetostrictive tube of the transducer head. The facsimile signals also include synchronizing pulses, one foreach scanning line, which are utilized to synchronize a high speed pulse generator at the reproducing system with the received facsimile signals. 'I he pulse generator excites the transverse elastic waves in the transducer head and controls the operation of the electronic switch.A

l The generator controls the electronic switch by introducirgits relatively highfrequency pulses to a modulator as a carrier together with relatively low-frequency pulses from al step-down counter driven by the generator as a modulating signal. The modulator output includes the carrier signal and upper and lower sideband signals. The output is filtered to provide a single sideband Vconsisting of pulses at a repetition rate which differs from the repetition rate of the generator bythe repetition rate of the step-down counter. The single sideband signal is utilized to actuate the electronic sampling switch.

Because of the difference in timing between the Asampled facsimile signals and the elastic waves, each elastic wave coincides with a sampled facsimile signal at successive incremental positions across the magnetic tape, I n this manner, a line of facsimile signals is recorded by means of a large number of overlapping transverse tracks across the magnetic tape. The recorded samples on the tape form one effective transverse track across the' tape triade u'p of a large number of elemental recordings, one, due to each successive elastic wave. The quality of the recording is high because of the large number of samples for eachl line.

l With each line scan' being recorded transversely across the tape, the successive recordings form a magnetic latent image `of the graphic material being scanned at the facsimile transmitter. The magnetic image is an enlargement with the enlarging ratio depending upon the tape width and the relative' speed of the tape with respect to the peripheral speed of the rotating drum at the transmitter.

Features of this' invention relate to the provision of means for producing a printed image' of the/,magnetically recorded image on the magnetic tap'e. The recorded tape passes' through magnetic inking apparatus which coats the magnetic tape with magnetic ink in accordance with the recording on the tape. The inked tape thereafter is engaged by suitable printing paperto' provide for a printed representation of the magnetically recorded picture. After thev printing sequence, the information still remains on the magnetic tape so that additional prints may be provided therefrom.v

Further advantages and features of this invention will become apparent upon consideration of the following description taken' in conjunction with the drawing where-` 1n: Y

FIGURE 1 is a functional representation of a portion of the facsimile reproducing system of this invention including a perspective view of the magnetic tape and transducer head;

FIGURE 2 is a longitudinal sectional view of the transducer head utilized in the facsimile reproducing system of this invention;

FIGURE 3 is a. sectional view of the transducer head taken through lines 3--3 of FIGURE 2;

FIGURE 4 is a pictorial view of the printing portion of the facsimile reproducing system of this invention; and

FIGURE 5 is a schematic diagram of equipment for progressing the magnetic tape adjacent the transducer head and through the printing portion of the facsimile reproducing system of this invention.

The facsimile reproducing system of this invention, which is shown partially in FIGURE 1, successively prints images of graphic material sampled at another location. The facsimile signals representing the graphic material are received at the receiving circuits 7 which provides them to an electronic sampling switch 8.

The facsimile signals are slow speed signals consisting of a synchronizing pulse for each scanned line followed by scanning line signals. The repetition rate of the synchronizing pulses and of the lines scans may be 120 per minute, with each line scan having a duration of 0.5 seconds.

The synchronizing pulses are separated from the scanning line signals by a pulse separator 30 which introduces them to a phase detector 31. The phase detector 31 cornpares the phase of the synchronizing pulses with the phase of pulses produced by a pulse divider or counter 32. The counter 32 is driven'by a high frequency pulse generator 33 having a nominal repetition rate of 100,000 pulses per second. The counter 32 provides one pulse to the phase detector 31 for each 50,000 pulses provided thereto from the generator 33 so that it has a nominal repetition rate of 2.0 pulses per second which is the repetition rate of the facsimile synchronizing pulses. If the phase of the synchronizing pulses changes, the detector 31 provides a direct-current error signal in accordance therewith to the generator 33. The generator 33 is adjustable and the error signal causes its repetition rate to change slightly to compensate for the difference in phase between the synchronizing pulses and the pulses from the counter 32.

For example, if the phase of the synchronizing pulses advances indicating that their repetition rate is increasing the repetition rate of the generator 33 increases to increase therewith the repetition rate of the counter 32. As the repetition rate of the counter 32 increases, the phase difference between the signals therefrom and the synchronizing signals reduces to reduce the error signal to the generator 33. In this manner, the pulse generator 33 is syn- A chronized with the facsimile signals received at the circuits 7.

The pulses from the generator 33 are also supplied to another pulse divider or counter 34 which divides the pulses from the generator 33 by a factor of 1,000. With the generator operating at a frequency of 100 kilocycles, the repetition rate of the counter 34 is 100 pulses per second. The 100 kilocycle signal and the 100 cycle signal are introduced to a modulator 35. The modulated output of the modulator 35 includes upper and lower sidebands and the 100 kilocycle carrier signals. The lower sideband and the carrier are removed by a filter 36 which passes the upper sideband signal at a frequency of 100,000 plus 100 or 100,100 cycles per second.

The pulses from the lter 36 are utilized to actuate the electronic switch 8 which samples the facsimile signals received at the circuits 7. The sampling rate is slightly higher than the repetition rate of the generator 33 because of the effect of the modulator 35 and the lter 36. Moreover, both the sampling rate and the repetition rate of the switch 8 are synchronized with the facsimile signals due to the self adjusting loop through the counter 32 and the detector 31.

The electronic switch 8 may be any one of a number of different switching or gating arrangements. One suitable switch is illustrated in FIGURE 319, page 54, of Waveforms, v. 19, Radiation Laboratories Series (McGraw- Hill, 1949).

The sampled signals from the switch 8 and also the pulses from the generator 33 by way of an amplifier 45 are introduced to a transducer head 11 which is positioned adjacent a magnetic tape 10. The transducer head 11 which is described in detail in my copending patent application, Serial No. 733,165, filed on May 5, 1958, is briefly described herein because it is an important component in the facsimile reproducing system of this invention.

The transducer head 11 which is shown more particularly in FIGURES 2 and 3 functions as a transverse recording head for the tape 10. As hereinafter described, the tape 10 moves longitudinally at a relatively slow speed adjacent the stationary transducer head 11. The tape transport equipment which is illustrated in FIGURE 5 includes a platform 13 which supports the head 11 by a bracket 12. The magnetic tape 10 is driven from a payout reel 14 adjacent the transducer head 11 through printing equipment 9 to a take-up reel 15. The magnetic tape 10 may be tensioned by individual motors, not shown, which drive the payout reel 14 and the take-up reel 15. l

From the payout reel 14, the magnetic tape 10 passes over a spring actuated tensioning arm 16 about which it turns at a substantially right angle to pass over a guide post 17. At the post 17, the magnetic tapeY 10 again makes a right angle turn to pass between a drive capstan 18 and a rubber-nip roller 19 and then against a cleaning device 20 to another guide post 21. The post 21 directs the magnetic tape 10 over the transducer head 11 at a particular angle relative to the periphery of the transducer head 11. The magnetic tape passes from the head 11 to the reel 15 along a path which is substantially the image of the path from the reel 14 to the head 11. The path from the transducer head 11 is over a post 23 between a nip-roller 24 and the drive capstan 18, post 28 and the spring actuated tensioned arm 29 through inking and printing equipment 9 to the take-up reel 15.

As shown particularly in FIGURES 2 and 3, the trans ducer head 11 includes a tube of magnetostrictive material which changes its magnetic properties with stress. The tube 40 which may be made of Pcrmalloy tape, has a nonmagnetic gap 41 extending longitudinally along the tube 40. Elastic waves are transmitted longitudinally through-r the magnetostrictive tube 40 by a piezoelectric crystal 42. responsive to voltage pulses developed by the pulse ampli-- lier 45. The pulses developed by the amplier 45 arev 0.1 microsecond in duration and have a repetition period equal to the repetition period of the pulse generator 33- At one end of the magnetostrictive tube 40, an acoustic: transformer section 46 is mounted to couple acoustic: waves generated by the piezoelectric crystal 42 to the?` magnetostrictive tube 40. The other side of the crystal. 42 is attached to an annulus 47 which functions as a buttress'against which the crystal 42 acts to deliver pulsed4 energy developed thereby to the acoustic transformer sec tion 46. The annulus 47 is in turn backed by an annulus. 48 of insulating material which is a good absorber off sound. The absorbent annulus 48 is in turn secured to a metal cap or nut 49 which is internally threaded to re ceive an adjusting screw 50.

At the opposite end of the magnetostrictive tube 40, a. cap 51 and an acoustic absorbent section 5-2 is mounted.. The waves generated from the crystal 42 are transmitted or propagated through the acoustic transformer section 46 and the magnetostrictive tube 40 at a speed of approximately 15,000 feet per second to the absorbing 'section 52. The structure including the magnetostrictive tube 40 is placed in tension by means of a strut 53 extending longitudinally through the tube 40 and bearing at one end in va depression formed in the inner end of the adjusting screw 50 and at the other end in a similar depression in the cap 5.1.

The effect of stress applied to the magnostrictive tube 40 due to the acoustic waves is to normally relax the tension or unstress the tube 40. The magnetostrictive tube 40 acts as though it were non-magnetic when it is stressed anti` it effectivelybecomes magnetic along the acoustic waves. Circumferential fields are induced by a signm Winding including the plated` sections 54 and 55 which are on the exterior and interior respectively of the magnetostrictive tube 40. In this manner, a moving recording gap is provided alongV the acoustic wave which changes the condition or successive position along the tube 40 from being eifectiively non-magnetic to being effectively magnetic. When the wave passes the successive positions return to their normal effectively non-magnetic conditions determinedA by the applied stresses. f

As indicated above, the facsimile signals are sampled by the electronic switch' 8 which supplies the sampled signals to a toroidal winding 215 ofy the transducer' head 11 which is coupled to the plated windings 54' andl 55.

The sampled signals are very short having a duration ofapproximately .l rnicrosecondv as determined' by the electronic switch 8. The transverse elastic pulses through the magnetostrictive tube 40 of the head 11 record the sampledv signals at a transverse position on the tape depending upon the timing therebetween. If the repetition rate of the sampled signals is exactly the same as that ofthe elastic Waves, the signals are recorded at the' same transverse position of the magnetic tape to form a single longitudinal track of recorded information. As described above, however', the repetition rate of the sampled signals is slightly larger than the repetition rate of the elastic waves. In order to provide an effective magnetic image of the graphic material, it is necessary toA record the sampled facsimile signals corresponding to one scanned line of lthe graphic material as a single-trans*- verse track on the magnetic tape 10. This is accomplished byV providing for a sampling rate which is slightly larger than that of the repetition rate of the enabling elastic pulses. Each enablingV pulse, therefore, coincides at a different successive position with one of the sampled signals.

Because the repetition rate of the sampled signals is slightly larger than that of the elastic waves, each successive sampled signal is recorded ata position on` the tape 10 just below that of its preceding signal. If the filter 36 removes the upper sideband signal insteadv of the lower sideband signal from the modulator 35i, the recorded signals advance transversely upthe tape 10 instead of transversely down across the tape 10. Either procedure provides for effectively recording the facsimile line as a large number of dots transversely across vthe tape 10; With' approximately 100,100 samples per line, the recording quality is very high and is equivalent to recording the facsimile signals in an uninterrupted manner.

With each line of the graphic `material being recorded as an eect-ive separate transverse track across the magnetic tape 10, the composite recording forms a magnetic latent image of the vgraphic material. The magnetic image maybe an enlargement of the graphic material which is scanned at the facsimile transmitter, not shown. The transverse dimension of the magnetic image on the tape 10 depends upon the wid-th of the tape 10 so that, providing a magnetic tape which is wider than the line dimension of the transmitted graphic material, provides for an enlargement thereof. For example, if the line dimension of the graphic material is 4 inches and the Width of the tape 10 is l2 inches, an enlarging ratio of 3 to l may be provided.- The other dimension of the graphic material, which is the longitudinal dimension of the tape 10, may be readily adjusted by changing the speed of the movement of the magnetic tape 10'.' Increasing ythe speed ofthe tape 10 effectively reduces the 6 over-lapping of the transverse tracks'due to successive elastic waves through the transducing head 11. By reducing the over-lapping, the effective transverse recording due to the successively recorded samplings of the facsimile signals is at a slightly greater angle to the longitudinal or direction of movement of the tape 10.

As shown in FIGURE 4, the tape passes from the pay-out reel 14,- also described above in reference to FIGURE 5, adjacent the transducer head 11 and then from the transducer head 11 to` magnetic inking apparatus 62. Actually, the paths from the reel 14 to the transducer head 1'1 and from the head 11 to the apparatus 62 are not linear as described above in reference to` FIGURE 5. A simplification of the path of the magnetic tape 10 is depicted in FIGURE 4 to illusstrate its movement from the head 11 through the inking apparatus' 62 to the take-up reel 15'.

The printing apparatus 62 includes a blower, tank or other apparatus for dispersing magnetic particles or ink such as carbonyl powder or the like on the magnetized surface of the magnetic tape 10. After the tape 10, therefore, passes through the apparatus 62, the magnetic powder or solution is disposed on its surface in accordance with its magnetization. The latent image on the tape 10 as recorded by the transducer head 11 is, therefore, visible as rthe tapel 10 emerges from the apparatus 62 As the tape 10 passesA from the nking apparat-us 62 to thel take-up reel 15, it is pressed against a printing paper 67'which is moving at the same speed asthetape 10' and the samedirection at thel point of contact. The paper 67 is driven from a pay-out roll 65 by the rollers 68 and 66 together withthe inking tape 10 and therefrom to a take-up roll 72. The paper 67 may be a wax or other type paper suitable for printing with the carbonyl powder or other magnetic ink. The take-up reel 15 for the tape 1-0 is driven by a motor 75 and the take-up roll 72 for the paper 67 may also be driven by the motor 75 through a linkage 73 or by a separate motor, not shown` As the ink is transferred from the tape 10 to the paper 67, thel tape 10' still retains the magnetic image so that additional prints may be readily provided.

Although this application has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible to numerous applications which may be apparent to persons skilled in the art. For example, in the event a print of the enlargement is not required but merely the pro-vision of a visible tape is adequate, the magnetic particles need not be suitable as a printing ink but may be of any type of magnetic substance. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

I claim:

1. ln a system for recording lines of information signals having a relatively slow repetition rate on a longitudinally moving recording medium, scanning means including transducing means disposed transversely of the medium to produce a scanning action upon the introduction of an enabling signal to such scanning means, recording means operatively associated with the transducing means for obtaining a recordingof sampled signals at progressive transverse positions dependent upon the 0peration of the scanning means, means operatively coupled to said scanning means for obtaining a controlled enabling of saidftransducing means to obtaina recording at a relatively fast track repetition rate, means responsive to said information signals for sampling the information signals, means coupled tothe sampling means and operatively associated with the recording means for introducing the sampled signals to said recording means to obtain the recording of the sampled signals at the position of enabling of the transducing means, means operatively coupled to said sampling means for controlling the operation of said sampling means at a rate which is greater than the line repetition rate of said' signals and different from the track repetition rate of said scanning means whereby successive sampled signals are recorded at successive transverse positions on different transverse tracks of the recording medium, and means coupled to said sampling means and to said enabling means for synchronizing said sampling means and said enabling means with the lines of information signals to obtain the recording of the lines of information signals in a particular pattern on the recording medium.

2. In a system for recording slow speed facsimile signals on a recording medium, high speed scanning means including transducing means disposed transversely relative to the recording medium and enabled at a high speed for producing a scanning action transversely across the medium upon each introduction of an enabling signal to such scanning means, recording means operatively associated with the transducing means for obtaining a recording of sampled signals at progressive transverse positions on the recording medium dependent upon the operation of the scanning means and in accordance with the sequential enabling of successive positions on the transducing means, sampling means coupled to said recording means for sampling the facsimile signals and for introducing such sampled signals to the recording means to obtain the recording of such sampled signals at the enabled positions of the transducing means, means including a pulse source coupled to said sampling means for operating said sampled means to sample the signals at intervals different than the recording interval of one transverse track by said transducing member, initiating means coupled to said transducing member for successively initiating transverse enabling waves in said transducing member at a frequency different from the sampling rate to Obtain a recording of the sampled signals at successive positions transversely across the recording medium, and means coupled to the sampling means and the initiating means for synchronizing the operation of the sampling means and the initiating means to obtain the recording of the facsimile signals in a particularpattern on the recording medium.

3. In a system for recording lines of a slow speed facsimile on a recording medium, scanning means including high speed transducing means disposed transversely relative to the recording medium to produce a scanning action upon the introduction of an enabling signal to such scanning means, recording means operatively associated with the transducing means for obtaining a recording of each line of the facsimile signals as a separate track on the recording medium in accordance with the enabling of said transducing means at successive positions along said transducing means, means coupled to said recording means for sampling the facsimile signal and for introducing the sampled signals to said recording means to obtain a recording by said transducing means at the positionvof enabling of said transducing means, means coupled to said sampling means for operating said sampling means at intervals smaller than the recording interval of one line of slow speed facsimile by said transducing means, means coupled to said transducing means for successively enabling said transducing means at a particular rate relative to the lines of slow speed facsimile whereby successively sampled signals are recorded at successive positions on the recording medium in accordance with the enabling of,

the transducing means at such successive positions, and

means operatively coupled to the enabling means and the sampling means and responsive to the lines of slow speed facsimile for synchronizing said enabling means and said sampling means with the lines of facsimile to obtain the recording of each line of facsimile in a particular pattern on the recording medium.

4. A transducing system for producing information signals representing scanned lines of graphic material on a recording medium, including, means for receiving the information signals,`sampling means coupled to said receiving means for successively sampling the information signals, scanning means including transducing means dis- ,Cil

posed transversely relative to the medium to produce a scanning action upon the introduction of an enabling signal to such scanning means, recording means operatively associated with the transducing means and the sampling means for obtaining a recording of the sampled signals at progressive transverse positions on the recording medium in accordance with the enabling of the transducing means at such transverse positions, enabling means coupled to said scanning means for periodically introducing enabling signals to the scanning means at a rate which is different than the sampling rate by said sampling means to obtain the sequential enabling of said transducer means at successive positions along said transducer means whereby said transducer means sequentially record said sampled signals at successive transverse positions across said transducer means, and means operatively coupled to said receiving means and to said enabling means for synchronizing said enabling means with said information signals to obtain the recording of each line of the information signals in a particular pattern on the recording medium.

5. A transducing system for recording on a recording medium an image of graphic material received in theY form of sequences of electrical signals each representing a synchronizing signal and a line scan of the graphic material, including, means responsive to the sequences of electrical signals for separating the synchronizing signals from said sequences of electrical signals, an adjustable pulse generator having a repetition rate greater than the repetition rate of said synchronizing signals, means coupled to said separating means and to said pulse generator for continuously adjusting the repetition rate of said generator in accordance with variations in the repetition rate of the synchronizing signals, scanning means including transducing means disposed transversely relative to the recording medium land enabled by said pulse generator to produce a scanning action constituting a sequential enabling of successive positions on the transducing means, recording means operatively associated with the transducing means to obtain a recording of the sequences of electrical signals on said recording medium in the form of an image of the graphic material at the positions of enabling of said transducing means, means responsive to the received sequences of electrical signals for sampling the received sequences of electrical signals, means coupled to said sampling means for operating said sampling means at 'a rate which is diiferent than the enabling rate of said v transducing means by said pulse generator, and means operatively coupled to said recording means and to said sampling means for introducing the sampled signals to said recording means whereby successive samples are recorded at successive transverse positions on said magnetic recording medium to form one track of recorded samples for each of the sequences of electrical signals.

6. A transducing system in Vaccordance with claim 5, including, a pulse divider coupled to said pulse generator for providing pulses at a repetition rate smaller than the repetition rate of said pulse generator, and means coul pled to said pulse generator and to said pulse divider for providingpulses at a repetition rate dependent upon the repetition rates of said generator and said divider, said sampling means including a switch controlled bysaid providing means for sampling said sequences of electrical signals.

References Cited in the le of this patent UNITED STATES PATENTS 2,668,283 Mullin Feb. 2, 1954 2,683,856 Kornei July 13, 1954 2,693,991 Holtz Nov. 9, 1954 2,762,861 Somers Sept. 11, 1956 2,780,774 Epstein Feb. 5, 1957 2,826,634 Atkinson Mar. 1l, 1958 2,836,650 Johnson .s May 27, 1958 2,890,275 Lesti June 9, 1959 2,943,908 Hanna July 5, 1960 

